Method for production of abrasive composition for use in toothpaste

ABSTRACT

The corrosion and staining of unlined aluminum tube surfaces by dentifrices such as toothpastes, particularly when the dentifrices contain therapeutic agents, is substantially prevented by incorporation into the dentifrice of a controlled amount of an alkaline earth metal ion such as calcium ion, in the range of 0.005-0.2 weight percent, and preferably in the range of 0.005-0.070 weight percent of the dentifrice. The alkaline earth metal may be provided from any water soluble alkaline earth metal salt or as a reaction product of the alkaline earth metal salt with an amorphous silica abrasive and/or thickener.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 946,678, filed Sept. 28, 1978now U.S. Pat. No. 4,244,707, which is a division of Ser. No. 826,901,filed Aug. 24, 1977, now U.S. Pat. No. 4,159,280 which is acontinuation-in-part of Ser. No. 723,345, filed Sept. 15, 1976, nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to dentifrice compositions and moreparticularly to dentifrice compositions such as toothpastes containingtherapeutic agents and/or polishing agents and other ingredients,wherein the composition also contains a controlled amount of alkalineearth metal ion to prevent corrosion and staining when placed in unlinedaluminum tubes over extended periods of storage.

2. Description of the Prior Art

Broadly speaking, there are two types of modern day dentifrices on themarket which may be described as opaque and clear-gel dentifricecompositions.

Each type of above mentioned dentifrice is marketed under two differentversions:

A. Cosmetic Type

B. Therapeutic Type

A cosmetic type toothpaste is one which contains no fluoride and ispromoted for whitening and brightening of the teeth. A therapeutictoothpaste, however, contains fluoride as anti-caries agent.

Therapeutic dentifrice compositions such as toothpaste normally containa fluoride therapeutic agent such as stannous fluoride,monofluorophosphate, or derivatives thereof, as well polishing agents,humectants, and other materials. These compositions are usually placedin aluminum or plastic tubes for sale on the commercial market. It isusually preferred to use aluminum tubes but it has been discovered thatwhen such toothpaste compositions contain a therapeutic fluoridecompound, a reaction with the interior of the unlined aluminum tubetakes place so that staining and other corrosive action occursapparently because of some reaction or incompatibility between the barealuminum surface and one or more of the materials in the toothpaste.This incompatibility appears in the form of gas production, swelling ofthe tube, corrosion, and black stains on the inside surface of unlinedaluminum container. Accordingly, the standard practice in the marketingof therapeutic toothpastes today has been to line the aluminum tube witha plastic, lacquer or other material, which therefore substantially addsto the cost of packaging and marketing the toothpaste.

Many prior art attempts have been made to solve this problem becauseunlined aluminum tubes are much more economical to use and are generallylighter in weight than the lined tubes. For example, U.S. Pat. Nos.3,662,060 and 3,624,199 disclose compositions which are said to overcomethis problem. Further, U.S. Pat. No. 3,678,155 discloses thatmonofluorophosphate ions prevent corrosion of unlacquered aluminum tubeswhen the toothpaste contains milled alpha-alumina trihydrates as anabrasive. Also U.S. Pat. No. 3,864,471 discloses a dentifricecomposition containing a monofluorophosphate and a polishing agentcontaining alkaline earth metal carbonate and insoluble alkali metalphosphate, alumina or mixture thereof, to minimize corrosion in unlinedaluminum containers.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to overcome orotherwise mitigate these problems of the prior art.

It is a further object of this invention to provide a novel toothpastecomposition which will not stain or otherwise corrode unlined tubes, anovel abrasive for use in such toothpaste and provide a method for thepreparation and packaging of a toothpaste composition in unlined tubeswhich will not cause corrosion and staining problems on the interior ofthe tube.

A still further object of the invention is to provide a non-corrosivetherapeutic toothpaste composition which contains a controlled amount ofalkaline earth metal ion so that the resulting composition can be placedin and marketed in unlined aluminum tubes.

Other objects and advantages of the present invention will becomeapparent as the description thereof proceeds.

In satisfaction of the foregoing objects and advantages there isprovided by this invention a therapeutic dentifrice compositioncomprising a fluoride-containing therapeutic agent, a polishing agent, aliquid phase, and about 0.005 to 0.20 weight percent of alkaline earthmetal ion per 100 parts of the toothpaste composition. Also provided isa novel polishing agent which can supply the alkaline earth metal ions.There is also provided by this invention an unlined aluminum tubecontaining dentifrice composition comprising a fluoride-containingtherape agent, a polishing agent, a liquid phase, and about 0.005 to0.20 parts of alkaline earth metal per 100 parts of toothpastecomposition. There is further provided by this invention a method forinhibiting the staining and corrosion of unlined aluminum tubes bytoothpaste compositions containing fluoride which comprises theincorporation within said toothpaste composition of about 0.005 to 0.20parts of alkaline earth metal per 100 parts by weight of said toothpastecomposition.

DESCRIPTION OF PREFERRED EMBODIMENTS

As pointed out above, since the introduction of therapeutic containingdentifrice compositions, it has not been possible to produce acommercially usable product which could be packaged in unlined aluminumtubes because of the incompatibility problems between the aluminumsurface of the tube and the other components of the dentifrice,particularly the fluoride. While substantial work has been carried outin an effort to overcome this problem as indicated by the prior artdiscussed above, problems in this area still persist. The presentinvention overcomes problems of this type in a commercially viablemanner and provides a fluoride-containing dentifrice or toothpastecomposition which can be packaged and sold in unlined aluminum tubes.

According to the present invention, it has been discovered that theproblem of corrosion of unlined aluminum tubes when formulated with atherapeutic dentifrice composition can be overcome by incorporationwithin the toothpaste composition of a controlled amount of an alkalineearth metal. The alkaline earth metal with which this invention isprimarily concerned is especially calcium, but there also may be usedmagnesium or strontium. Calcium is preferred because of its readyavailability, inexpensiveness and ease of incorporation into thedentifrice. The metal may be incorporated into the dentifrice ortoothpaste mixture in any substantially water soluble form such as thenitrate, oxide, hydroxide or chloride. The most preferred materials forincorporation into the therapeutic dentifrice compositions of thisinvention include calcium nitrate, calcium oxide, calcium hydroxide, andcalcium chloride. It should also be noted however, that organic saltssuch as calcium acetate, calcium formate and the like may also be used.Corresponding strontium and magnesium salts may also be used. The onlylimitations to be placed on the alkaline earth metal salt are that it besubstantially soluble, not cause any problems of safety in thecompositions, and remain available to combat corrosion.

There are of course dentifrice and other toothpaste compositions knownin the art which contain calcium salts in substantial amounts, as taughtfor example in U.S. Pat. No. 3,864,471 which contains 40-50% of calciumcarbonate and U.S. Pat. No. 3,624,199 which contains 20-75% calciumcarbonate. However, calcium carbonate is generally insoluble, and is noteffective to inhibit corrosion of the tube. Therefore, an importantaspect of the present invention resides in the carefully controlledamount of water-soluble alkaline earth ion which is incorporated intothe toothpaste composition. According to the present invention, thecontrolled amount of alkaline earth metal ion which is present must besufficient to be effective and available to prevent corrosion but yetinsufficient to stoichiometrically interfere with fluoride availabilityin the toothpaste. According to the present invention, it has been foundthat the amount of alkaline earth metal which must be present to preventcorrosion is at least about 50 parts per million, or 0.005 weightpercent, and not more than about 2000 parts per million, or 0.2 weightpercent, should be present to avoid interference with fluorideavailability. Therefore, the amount of alkaline earth metal which shouldbe present should range from about 50-2000 parts per million or 0.005 to0.2 weight percent based on the toothpaste.

As pointed out above, the alkaline earth metal ion may be incorporatedinto the toothpaste as any water soluble salt. However, it is alsowithin the scope of the present invention to supply the alkaline earthmetal ion in combination with silica and silicate type abrasive and/orpolishing agents. According to one aspect of this embodiment, acontrolled structure amorphous precipitated silica may be incorporatedinto the therapeutic composition in sufficient amounts to supply thenecessary alkaline earth metal, such as calcium ion, to overcome theproblems of corrosion and staining. These dentifrice grade controlledstructure precipitated silicas contain calcium ions on the silicasurface of the precipitated silica abrasive, polishing agent orthickening agent.

The dentifrice grade controlled structure precipitated silicas orsilicon dioxides referred to above are novel products available from theJ. M. Huber Corporation and are silicon dioxide products of the typedescribed for example in my U.S. Pat. Nos. 3,960,586 and 3,928,541 whichhave been treated with an alkaline earth metal salt to provide thealkaline earth metal ions in the composition. The products described inthese patents are precipitated silicic acid or silicon dioxide pigmentswhich are prepared by the acidulation of an alkali metal silicate suchas sodium silicate and an acid such as sulfuric acid, in the presence ofa salt or electrolyte such as sodium sulfate. The precipitated silicasresulting from the reaction wherein the sulfate is a necessary reactantin the process may be described as sulfate liquor products. Afterpreparation of the precipitated silica in wet cake form, and washing, itis then reslurried in water and treated with a soluble alkaline earthmetal salt such as calcium hydroxide, calcium oxide, calcium nitrate, orcalcium chloride, in sufficient amounts to incorporate the necessaryamount of alkaline earth metal ions directly into the silica. Thereaction of silica with alkaline earth metal is conducted at ambienttemperature and with agitation. The amount of alkaline earth metal ionsintroduced will be sufficient to provide the required amount of alkalineearth metal ions in the toothpaste but is correlated with any desiredamount of alkaline earth metal ions incorporated directly into thetoothpaste composition.

It will be understood therefore that the amorphous silica material ispretreated with the critical level of alkaline earth metal material andthen incorporated into the toothpaste composition in the requisiteamounts as desired. These silica compositions provide good cleaningproperties at RDA values of between 200-400. (RDA-Grabbenstetter et al,Jour. of Dental Research, 37, 1060, 1958).

The precipitated silicon dioxide of the present invention are preferablyprepared by charging a 3-15 weight percent aqueous solution of alkalimetal sulfate, preferably sodium sulfate, to a reactor and adding asolution of an alkali metal silicate solution, preferably a sodiumsilicate solution, to the reactor to achieve a pH of about 8-10.4. Thisresults in pre-polymerization of the alkali metal silicate. The aqueoussodium silicate solution should have a silicate concentration range ofabout 10-25 weight percent, and more preferably 18 to 22 weight percent,and a composition of Na₂ O.2.6 SiO₂ for best results. The aqueoussolution is then raised to a temperature of about 66° to 83° C. (150° to180° F.) and with continuous agitation the solution is acidulated by theaddition of an aqueous solution of a mineral acid having a concentrationof about 10-25 weight percent at a substantially constant pH in therange of about 8.0 to 10.4. Preferably the mineral acid and alkali metalsilicate are added simultaneously as described in my U.S. Pat. No.3,960,586. For purposes of preparation of the basic precipitated silicaor silicon dioxide, the disclosures of my prior U.S. Pat. Nos. 3,960,586and 3,928,541 are expressly incorporated herein by reference. Themineral acid is preferably sulfuric acid as sulfuric acid provides bestresults but as known in the art as in my prior U.S. Pat. No. 3,960,586,other acidulation agents such as nitric acid, phosphoric acid,hydrochloric acid, carbonic acid and the like may also be employed. Thetime period over which the alkali metal silicate and/or sulfuric acidare added to the reactor can be predetermined and is generally based onthe volume of the reactor and the difficulties in control on the volumeof the reactor and the difficulties in control of the temperature andagitation. After completion of the additions, the acidulation acid iscontinued to be added until the pH of the slurry falls below about 6.0and preferably in the range of about 4.8-5.0. The resulting slurry isthe precipitated silicon dioxide contained in the reaction medium.

After the pH of below 6.0 is obtained, the slurry is then heated for adigestion period of 10 to 30 minutes at a temperature of 10° to 30° C.above the reaction temperature and the reaction pH again adjusted asnecessary. The resulting slurry is then filtered and washed withadditional water to remove any reaction by-product such as sodiumsulfate which may be contained in the silicon dioxide product.

In the process of the present invention, at the point of filtration andwashing of the silicon dioxide wet cake, the material is then subjectedto treatment with alkaline earth metal ions to produce the new abrasiveproducts of the present invention. In accordance with the process of thepresent invention, the wet wash filter cake is then reslurried in itsown water or with the addition of fresh water at ambient temperaturewith agitation. While under agitation, this slurry is then treated withsufficient alkaline earth metal ions and preferably calcium ions, in theform of substantially soluble salt to provide sufficient alkaline earthmetal ions corresponding to provide about 50 to 2000 parts per million,intimately associated with the silicon dioxide, this amount being basedon 100 parts of dentifrice. The amount of alkaline earth metal ionsadded is based on the total weight of the dry product contained in thewet cake form, that is recoverable solid. Since the amount of abrasivemay vary in dentifrice compositions, the amount of alkaline earth metalsalt will also be varied.

The alkaline earth metal ion added at this point is preferably calciumion because of its readily availability, inexpensiveness and ease ofincorporation into the silicon dioxide. The calcium ions may beincorporated into the silicon dioxide at this stage in any substantiallywater soluble form such as the nitrate, oxide, hydroxide, or chloride,but lime or calcium hydroxide is preferred. Food grade salts should beused. By soluble salts is meant that any reasonably soluble salt ofcalcium may be used since it is only necessary to provide extremelysmall amounts of the calcium ions to the mixture. Also, organic saltssuch as calcium acetate, calcium formate, and the like may also be used.The corresponding strontium and magnesium salts of the alkaline earthclass may also be used. The only limitations to be placed on thealkaline earth metal salt to be added are that it be sufficiently watersoluble to provide the ions, not present any problems of safety in theresulting toothpaste compositions, and be effective to provide thenecessary fluoride compatibility.

After treatment with the alkaline earth metal ion, the cake slurry isthen agitated vigorously for 10-20 minutes, preferably 15 minutes, toprovide the effective level of alkaline earth metal for treatment on thesurface of the silicon dioxide abrasive. The resulting product is thenfiltered, spray dried preferably at an inlet temperature of 483° C.(900° F.) and outlet temperature of 122° C. (250° F.) as known in theart, and subsequently milled to the desired degree of fineness.

The precipitated amorphous silicas which are preferably used in thisembodiment may be characterized by the following combinations ofproperties:

Oil Absorption-Rub-Out Method (cc/100 g)=80-120

BET Surface Area (m² /g)=75-325

MSA Average Aggregate Size (micron)=1-10

Bulk Density (lbs./cu.ft.)=10-30

Another precipitated amorphous silica that may be used in thisembodiment has the following properties: a pack density of about 0.24 to0.51 grams per milliliter, an oil absorption of about 75-95 ccs/100grams, a BET surface area of about 100-250 m² /g, and a percent loss onignition of about 4-6%.

It is also to be understood however, that the invention includes othertypes of silica polishing agents including Xerogels as described in U.S.Pat. No. 3,538,230. Commercially available Xerogels such as Syloid 63,manufactured by Davison Division of W. R. Grace & Co., can be utilizedwhen incorporated with controlled amounts of calcium ion or alkalineearth metal ions or pretreated with calcium ion or alkaline earth metalions, as described here. It is also to be understood that sodiumaluminosilicate polishing agents can be formulated in therapeuticcompositions according to this invention when the sodium aluminosilicatematerials are combined with the critical amounts of alkaline earth metalas described herein.

As known in the art, a dentifrice may contain; e.g., humectant materialsand binders to give the dentifrice a smooth texture and goodflowability. The specific formulations of toothpastes are well known inthe art and are disclosed for example in U.S. Pat. Nos. 2,994,642 and2,538,230 and numerous publications. A further detailed disclosure ofdentifrice formulations is given in U.S. Pat. No. 3,726,961.

In this regard, dentifrice formulations have been produced, ranging fromliquids and powders to the highly popular pastes or dental creams.Dental creams are the more difficult to compound successfully in thatthey require careful balancing of polishing agent, humectant, water,binder, preservatives, detergents, flavoring, sweeteners, andtherapeutic agents to produce a smooth homogeneous paste.

Most dental cream formulations use one of several conventional phosphatematerials as the polishing agent. Examples of the phosphate polishingagents are dicalcium phosphate, anhydrous dicalcium phosphate,tricalcium phosphate, thermally converted dicalcium phosphate, andinsoluble sodium metaphosphate. The amount of phosphate materials addedto the dental formulations will range between about 5 percent and 60percent by weight.

The most widely used humectants in toothpaste are glycerine andsorbitol. Propylene glycol is also used in small amounts and to a verylimited extent. The primary function of humectant as part of the liquidphase is to retain moisture which provides good texture and maintains anattractive glossy appearance when the paste is exposed to air.

The binder employed therein is to prevent separation of the liquid andsolid phases. The most conventionally used binders are the seaweedcolloids and synthetic derivatives of cellulose, specificallyCarrageenan and sodium carboxymethyl cellulose. Others such as gums havebeen used. Combinations of these binders have also been employed.

Since the natural and synthetic water dispersions of organic binders aresubjected to microbial or mold attack, a relatively small amount ofpreservatives is added to the paste. Examples of preservatives used inthe industry are the esters of parahydroxyl benzoates.

The function of the detergents within the dental formulation is toprovide greater cleansing action due to the lowering of the surfacetension and the sudsing action in the mouth. Among detergents used aresodium N-lauryl sarcosinate, sodium lauryl sulfate, sulfoculaurate,sodium alkyl sulfoacetate, and sodium dioctyl sulfosuccinate.

Since toothpaste flavoring probably represents the greatest singlefactor in consumer acceptance, great care has been employed in selectingbalanced blends of different essential oils. These are rarely, if ever,used aone. Combinations of principal flavors are wintergreen,peppermint, and sassafras, and are used with secondary oils such aspimento, clove and anise.

Saccharin and sodium cyclamate are widely used to improve taste andenhance the flavor qualities of the toothpaste. The synthetic sweetenersmay be used in combination to obtain optimum sweetness and absence ofafter-taste. Their desirable properties are obtained at very lowconcentrations and consequently they have negligible influence on thetoothpaste consistency.

Since water is such a common element, it is important in obtainingstable toothpaste formulations to employ substantially pure watertherein. It is common practice to demineralize the water that isemployed.

It is also within the scope of the invention to provide the properamount of alkaline earth metal within the dentifrice composition bypretreating the water with the calcium or alkaline earth metal so thatthe water used can serve as the alkaline earth metal source.

The invention is operable with respect to any of the therapeutic agentsnow being used in therapeutic dentifrice compositions including thealkali metal fluorides such as sodium fluoride, sodiummonofluorophosphate, stannous fluoride, and the like, all of which arewell known.

In general, such dentifrice compositions will normally contain about5-50 wt% of polishing agent, up to about 1 wt% of fluoride-containingtherapeutic agent, about 30-40 wt. % deionized water, and the remainderbeing liquid phase carrier materials such as glycerin, sorbitol and thelike. As indicated above, according to the present invention, thecomposition will also contain from 0.005 up to 0.20 wt % of alkalineearth metal ion, preferably calcium ion, based on the toothpastecomposition. It has been found that this amount of alkaline earth metalis sufficient to overcome problems with staining and corrosion ofunlined aluminum tubes, but is insufficient to interfere with thefluoride availability in the paste and thus not interfere with thetherapeutic action of the dentifrice composition.

With respect to incorporation of the controlled amount of alkaline earthmetal in the compositions of the present invention, it is to be notedthat in Degussa Technical Bulletin No. 9, there is a disclosure of an"Aerosil 200" polishing agent for use in chalk toothpastes, and it ispointed out on page 8 of this Bulletin that in toothpastes containingthe cheaper polishing agent, chalk, the use of "Aerosil 200" isworthwhile to the extent that the less expensive unlacquered aluminumtubes can be used since corrosion protection for unlacquered aluminumtubes is by formation of minute quantities of insoluble calcium silicatefrom this composition. A minimum of 1% of "Aerosil 200" is required.However at page 8 of the same Bulletin, it is stated that even with theuse of "Aerosil", it is not possible to attain effective corrosionproduction for nontreated aluminum tubes when the toothpastecompositions contain fluorine in the form of monofluorosodium phosphate.However, this reference does teach on page 8, that when 3-5 weightpercent of Light Hydrated Alumina W-16 is incorporated into thefluoride-containing toothpaste, corrosion protection can be obtained.Contrary to the teachings of this Technical Bulletin, it has beendiscovered according to the present invention that fluorine-containingtoothpastes can be placed in unlined aluminum tubes if there is placedtherein a controlled amount of alkaline earth metal ion.

In consideration of the incorporation of silica type products in thedentifrice composition of the present invention, it will be understoodthat all silica products and raw materials have incidental amounts ofcalcium present. For example, trade publications covering the Xerogelssold as Syloid 63 indicate the presence of 0.01% calcium as calciumoxide. This corresponds to 0.007% calcium or up to 70 parts per millionin Syloid 63. However, since only about up to 35 weight percent levelsof the silica products can be incorporated into toothpaste compositions,this indicates that inherently, the resulting dentifrices can containonly 0.0035 of calcium oxide or 25 ppm of calcium, an insufficientamount for corrosion protection. It will also be noted that theprecipitated silicas of J. M. Huber Corporation as described above, havea tendency to pick-up or react with calcium ions which make theseproducts extremely attractive for combination with the correct amount ofcalcium ions and incorporation into toothpastes since the silicas alsoprovide excellent abrasion properties for toothpaste compositions.

The silica abrasives described herein are used at loadings of about15-30 wt % in the dentifrice. Therefore they should contain a minimum of168 ppm calcium at 30 wt % and 336 ppm at 15 wt % to provide minimumamounts of calcium. However, they can also contain up to about 7000 ppmor more.

The following specific examples are further illustrative of the natureof the present invention, but it is to be understood that the inventionis not limited thereto. The compositions are prepared in theconventional manner and all amounts of the various ingredients are byweight unless otherwise specified. In the following examples andthroughout the specification parts are by weight unless otherwiseindicated.

EXAMPLES

In the following examples the toothpaste compositions were prepared andcompared with commercial products or controls. In evaluating thetoothpaste compositions, a chart was used to rate the interior tube wallto determine the presence or absence of staining and corrosion. As basisfor the chart, each composition was prepared and then aged at 49° C. fornine weeks. The percentage of soluble fluoride ion and tubecompatibility data were determined periodically during the nine-weekstorage stability period. In this examination, each three weeks underthe aging conditions (49° C.) corresponds to about one year aging atroom temperature. During the studies the unlined tubes containing thecompositions were opened periodically and examined for anystaining/corrosion on the tube interior wall. The following legend wasused for rating the tube properties of the compositions:

    ______________________________________                                        Rating     Tube Interior Wall                                                 ______________________________________                                        10         No air on wall, no discoloration on wall                           8-9        No air on wall, light gray stain on wall                           6-7        Air on wall, light gray stain on wall                              1-5        Air on wall, gray stain on wall                                    2-3        Air on wall, dark gray stain on wall                                1         Air on wall, black stain with pitting of                           ______________________________________                                    

In all of the following examples, the alkaline earth metal was calciumand was added as soluble calcium nitrate to provide the amount ofcalcium indicated in each composition.

EXAMPLES 1-4 Dentifrice Compositions in Which Calcium Was Added to theToothpaste

The following dentifrice compositions were prepared with a low structuresilica polishing agent and a known level of calcium was added to thecomposition to provide tube compatibility properties.

    __________________________________________________________________________                   Examples 1-4                                                                  Composition                                                                   1     2     3     4                                            __________________________________________________________________________    Sodium monofluorophosphate                                                                   0.76  0.76  0.76  0.76                                         Low Structure silica                                                                         30.00*                                                                              29.970                                                                              29.941                                                                              29.587                                       Calcium as water soluble                                                      Ca(NO.sub.3).sub.2 . 4H.sub.2 O**                                                            0.00  0.0295                                                                              0.059 0.413                                        Glycerine      23.00 23.00 23.00 23.00                                        Sodium carboxymethyl-                                                         cellulose      1.30  1.30  1.30  1.30                                         Hydrated alumina                                                                             1.00  1.00  1.00  1.00                                         Sodium lauryl sulfate                                                                        2.00  2.00  2.00  2.00                                         Sodium benzoate                                                                              0.50  0.50  0.50  0.50                                         Sodium Saccharin                                                                             0.20  0.20  0.20  0.20                                         Flavor         0.90  0.90  0.90  0.90                                         Water (deionized)                                                                            Balance                                                                             Balance                                                                             Balance                                                                             Balance                                      Total          100.00                                                                              100.00                                                                              100.00                                                                              100.00                                       __________________________________________________________________________      *low structure silica containing 5 ppm calcium                                **The conversion factor for calcium nitrate . 4H.sub.2 O to calcium is       5.9. The molecular weight of Ca(NO.sub.3).sub.2 . 4H.sub.2 O is 236. The      atomic weight of calcium is 40. Therefore 236 parts of calcium nitrate .      4H.sub.2 O provide 40 parts of calcium ion, of 236/40 or 5.9 parts of         calcium nitrate . 4H.sub.2 O, which corresponds to one part of calcium.  

In compositions 2, 3, and 4, calcium nitrate.4H₂ O was added in thedentifrice composition which corresponds to calcium level of 0.0295/5.9or 50 ppm (0.005%); 100 ppm (0.01%) and 700 ppm (0.07%), respectively.The tube compatibility data for these Examples are set forth infollowing Table 1.

                  TABLE 1                                                         ______________________________________                                        Rating of Tube Properties - 49° C. Aging Study                                Weeks                                                                  Composition                                                                            0       1        3      6      9                                     ______________________________________                                        1        10      4        3      3      1                                     2        10      10       10     10     10                                    3        10      10       10     10     10                                    4        10      10       10     10     10                                    ______________________________________                                    

It is clear from above data that composition 1 was unacceptable in tubecompatibility properties because it did not contain the minimum criticallevel of calcium in the therapeutic dentifrice composition.

EXAMPLES 5-8

The following dentifrice compositions were prepared wherein the contentof sodium monofluorophosphate in each is equivalent to 0.1% fluorideion.

    __________________________________________________________________________    Composition    Parts                                                          __________________________________________________________________________    Sodium monofluorophosphate                                                                   0.76    0.76    0.76    0.76                                   Low Structure silica                                                                         30.00(A)                                                                              30.00(B)                                                                              30.00(C)                                                                              30.00(D)                               Glycerine      23.00   23.00   23.00   23.00                                  Sodium carboxymethyl-                                                         cellulose      1.30    1.30    1.30    1.30                                   Hydrated alumina                                                                             1.00    1.00    1.00    1.00                                   Sodium lauryl sulfate                                                                        2.00    2.00    2.00    2.00                                   Sodium benzoate                                                                              0.50    0.50    0.50    0.50                                   Sodium saccharin                                                                             0.20    0.20    0.20    0.20                                   Flavor         0.90    0.90    0.90    0.90                                   Water (deionized)                                                                            40.34   40.34   40.34   40.34                                  Total          100.00  100.00  100.00  100.00                                 __________________________________________________________________________     (A) low structure silica of composition 5 contained 5 ppm calcium             (B) low structure silica of composition 6 contained 168 ppm calcium           (C) low structure silica of composition 7 contained 406 ppm calcium           (D) low structure silica of composition 8 contained 688 ppm calcium      

The low structure silicas employed in Examples 5, 6, 7 and 8 werecharacterized by the following combination of propert

Oil Absorption-Rub-Cut Method (cc/100 mg)=80-120

BET Surface Area (m² /g)=75-325

MSA Average Aggregate Size (microns)=1-10

Bulk Density (pounds/cu.ft.)=10-30

The calcium treated low structure silicas of compositions 5, 6, 7 and 8were prepared by the following procedure:

Dry sodium sulfate was added to 10.0 gallons of water in a 200 gallonreactor so that the sodium sulfate concentration in the reaction mediumwas 10%. The pH of the reaction medium was then adjusted to 9.0 by theaddition of sodium silicate. The reaction temperature was 65° C. (150°F.). The sodium silicate solution had an SiO₂.Na₂ O mole ratio of 2.5and a concentration of 2.0 pounds per gallon. Sodium silicate was addedto the reaction medium for 4 minutes. At this point the sodium silicateaddition was stopped and sulfuric acid of 11.4% concentration was addedto the reaction medium until the pH of 9.0 was reached. At this pointthe sodium silicate solution and the sulfuric acid solution was addedsimultaneously for a period of 35 minutes. At the end of the 35 minuteperiod of silicate addition, the silicate was discontinued and the acidaddition was continued until a slurry pH of 5.5 was obtained. The batchwas digested at 77° C. (170° F.) for 20 minutes and the resulting wetcake recovered and washed.

The wet cake was then divided into four separate portions and treated bythe following procedure.

Each batch of wet wash filter cake was then reslurried without wateraddition at ambient temperature with agitation. While under agitation,the slurry was treaed with sufficient Codex grade (U.S. purity foodgrade) hydrated lime (calcium hydroxide) to provide the amount ofcalcium ion treatment described in compositions 5, 6, 7 and 8. Theamount of calcium hydroxide was based on the weight of dry recoverablesolid product in the wet cake form. After treatment with the calciumion, the cake slurry was agitated vigorously for 15 minutes to providethe effective level of calcium ion treatment on the surface of thesilicon dioxide abrasive. Each resulting product is then spray dried atan inlet temperature of 483° C. and outlet temperature of 122° C. milledand characterized.

Compositions 5, 6, 7 and 8 were aged at 49° C. for nine weeks and tubecompatibility data were determined periodically during the nine-weekstorage stability period. The results for tube compatibility propertiesare listed below in Table 2.

                  TABLE 2                                                         ______________________________________                                        Rating of Tube Properties - 49° C. Aging Study                                Weeks                                                                  Composition                                                                            0       1        3      6      9                                     ______________________________________                                        5        10      4        3      3      1                                     6        10      10       10     10     10                                    7        10      10       10     10     10                                    8        10      10       10     10     10                                    ______________________________________                                    

It will be noted from Table 2 that dentifrice composition 5 caused asevere degree of black stain and pitting on the tube wall after nineweeks of aging study. Compositions 6, 7 and 8 were stable and showedexcellent tube compatibility properties. Thus, it is very clear thatwhen a silica polishing agent contains a minimum critical level ofcalcium, it does not corrode the unlined aluminum tubes.

EXAMPLES 9-11 Stabilization of Xerogel Therapeutic Dentifrices withCalcium

Therapeutic dentifrices were prepared with xerogel polishing agents. Allcompositions contained a known level of calcium ions (added as watersoluble calcium nitrate) except composition 9. The compositions wereprepared in the conventional manner and packaged in unlined aluminumtubes. All amounts of the various ingredients were by weight unlessotherwise specified.

The following dentifrice compositions were prepared. The content ofsodium monofluorophosphate in each was equivalent to 0.1% fluoride ion.

    ______________________________________                                                         Parts                                                        Composition        9        10      11                                        ______________________________________                                        Glycerine (99.5% solution)                                                                       22.00    22.00   22.00                                     Sodium benzoate    0.50     0.50    0.50                                      Sodium saccharin   0.20     0.20    0.20                                      CMC - 7 MF         1.00     1.00    1.00                                      Sodium monofluorophosphate                                                                       0.76     0.76    0.76                                      Water (deionized)  36.54    36.54   36.54                                     Xerogel (Syloid 63)                                                                              35.00    34.82   34.70                                     Hydrated alumina   1.00     1.00    1.00                                      TiO.sub.2          0.50     0.50    0.50                                      Sodium lauryl sulfate                                                                            1.50     1.50    1.50                                      Calcium nitrate . 4H.sub.2 O*                                                                    0.00     0.18    0.30                                      Flavor             1.00     1.00    1.00                                      ______________________________________                                          *0.18% and 0.30% calcium nitrate . 4H.sub.2 O in compositions 10 and 11      correspond to 0.18/5.9 or 0.03% calcium (300 ppm calcium) and 0.30/5.9 or     0.05% calcium (500 ppm calcium)                                          

It will be noted that the composition of Example 9 did not contain anycalcium. The tube properties were then determined when the dentifriceswere aged at 49° C. for nine weeks and were rated at intervals of 1, 3,6, and 9 weeks. The following Table 3 shows the degree of corrosion orstaining of the unlined aluminum tubes.

                  TABLE 3                                                         ______________________________________                                        Tube Compatability Properties - 49° C. Aging Study                            Weeks                                                                  Composition                                                                            0       1        3      6      9                                     ______________________________________                                         9       10      7        6      6      6                                     10       10      10       10     10     10                                    11       10      10       10     10     10                                    ______________________________________                                    

From the data in Table 3 it is clear that the compositions of Examples10 and 11 exhibit excellent tube compatibility properties. Note thatrating of 10 means no discoloration of the unlined tube container. Sincecomposition 9 did not contain the critical level of calcium, the tubecompatibility properties were found to be unacceptable after nine weeksstorage at 49° C.

According to the suppliers bulletin, the Xerogel, Syloid 63, has thefollowing properties:

Loss on ignition: 6.5

5% slurry pH: 4.1

% SiO₂ ignited basis: 99.5

Particle size, microns: 9.0

Surface area m² /g: 625

Oil absorption, #/100 lb: 60

Bulk density, pounds/cu. ft.: 29

In addition to above properties, Syloid 63 has the following chemicalcomposition (from supplier's bulletin):

    ______________________________________                                        Chemical Analysis (dry basis)                                                                      %                                                        ______________________________________                                        Aluminum as Al.sub.2 O.sub.3                                                                       0.04                                                     Titanium as TiO.sub.2                                                                              0.03                                                     Calcium as CaO       0.01                                                     Sodium as Na.sub.2 O 0.02                                                     Zirconium as ZrO.sub.2                                                                             0.01                                                     Trace element (oxides)                                                                             0.02                                                     ______________________________________                                    

EXAMPLE 12 Effect of Calcium on Commercial Toothpastes

"Aim" clear-gel therapeutic toothpaste is packaged in a lined containerto prevent corrosion and staining of tube interior wall.

"Colgate Dental Cream" (CDC) is also packaged in a lined container toavoid the corrosion and staining of the tube interior wall.

To check the effectiveness of calcium addition in solving the tubecompatibility problem, both "Aim" and "CDC" were purchased from thesupermarket and each paste was divided into three parts.

"Aim" toothpaste was divided in parts A, B, and C. Part A was packagedin an unlined aluminum tube without any addition of calcium to thetoothpaste. Parts B and C were mixed with a known level of calcium andthen packaged in unlined aluminum tubes.

"CDC" (Colgate Dental Cream) was also divided into three parts D, E, andF. Part D was packaged in an unlined aluminum tube without the additionof any calcium. To parts E and F, a known level of calcium was added.The data obtained with "Aim" and "CDC" compositions packaged in unlinedcontainers are listed in Table 4 and the compositions for each are asfollows:

    ______________________________________                                                                   Commercial                                         Composition % Calcium.sup.(3)                                                                            % Dentifrice                                       ______________________________________                                        A           0.00           100.00.sup.(1)                                     B           0.10           99.41.sup.(1)                                      C           0.16           99.16.sup.(1)                                      D           0.00           100.00.sup.(2)                                     E           0.10           99.41.sup.(2)                                      F           0.16           99.16.sup.(2)                                      ______________________________________                                         .sup.(1) Aim toothpaste, purchased from supermarket                           .sup.(2) Colgate Dental Cream, purchased from supermarket                     .sup.(3) Added at Ca(NO.sub.3).sub.2 . 4H.sub.2 O                        

                  TABLE 4                                                         ______________________________________                                        Tube Compatibility Properties - 49° C. Aging Study                            Weeks                                                                  Composition                                                                            1         3         6       9                                        ______________________________________                                        A        5         4         3       1                                        B        10        10        10      10                                       C        10        10        10      10                                       D        5         5         4       2                                        E        10        10        10      10                                       F        10        10        10      10                                       ______________________________________                                    

Compositions B, C, E and F have excellent tube compatibility propertieswhen compared with compositions A and D. The addition of the calciumthus helped stabilize these therapeutic dentifrice compositions.

EXAMPLES 13-17

The following dentifrice compositions were prepared to illustrate theuse of sodium aluminosilicates (SAS) as polishing agents. Thecomposition of Example 13 was used as a control in which no calcium wasadded. Known amounts of calcium were added to the compositions ofExamples 14, 15, 16 and 17. The compositions were as follows:

    __________________________________________________________________________                Parts                                                             Composition                                                                              13      14     15     16     17                                    __________________________________________________________________________    Glycerine (99.5%)                                                                         22.00  22.00  26.00  25.00  30.00                                 Sodium benzoate                                                                           0.50   0.50   0.50   0.50   0.50                                  Sodium saccharin                                                                          0.20   0.20   0.20   0.20   0.20                                  CMA - 7 MF  1.00   1.00   1.00   1.00   1.00                                  Sodium monofluoro-                                                            phosphate   0.76   0.76   0.76   0.76   0.76                                  Calcium nitrate . 4H.sub.2 O*                                                             0.00   0.20   0.20   0.20   0.24                                  Deionized water                                                                           36.54  36.24  39.54  38.54  43.30                                 SAS Polishing agent                                                                       35.00(A)                                                                             35.00(A)                                                                             27.80(B)                                                                             29.80(C)                                                                             20.00(D)                              Hydrated alumina                                                                          1.00   1.00   1.00   1.00   1.00                                  TiO.sub.2   0.50   0.50   0.50   0.50   0.50                                  Sodium lauryl sulfate                                                                     1.50   1.50   1.50   1.50   1.50                                  Flavor      1.00   1.00   1.00   1.00   1.00                                  __________________________________________________________________________     *Note that in compositions 14, 15 and 16 0.2% Ca(NO).sub.3).sub.2 .           4H.sub.2 O corresponds to 0.03% calcium ion and 0.24% Ca(NO.sub.3).sub.2      4H.sub.2 O in composition 17 corresponds to 0.04% calcium ion.                (A) The SAS product used in compositons 13 and 14 has a SiO.sub.2             /Al.sub.2 O.sub.3 ratio of 11.0.                                              (B) The SAS product used in composition 15 has a SiO.sub.2 /Al.sub.2          O.sub.3 ratio of 2.5                                                          (C) The SAS product used in composition 16 has a SiO.sub.2 /Al.sub.2          O.sub.3 ratio of 130                                                          (D) The SAS product used in composition 17 has a SiO.sub.2 /Al.sub.2          O.sub.3 ratio of 400                                                     

The preferred sodium aluminosilicates (SAS) have the following molarchemical composition:

    x Na.sub.2 O.y Al.sub.2 O.sub.3.z SiO.sub.2.w H.sub.2 O

wherein

x denotes the moles of Na₂ O

y denotes the moles of Al₂ O₃

z denotes the moles of SiO₂

w denotes the moles of water

When y is fixed at 1, the value of z corresponds to the silica/aluminamolar ratio of SAS. The low structure SAS abrasives and polishing agentshave a silica/alumino ratio or z values of 2.5 to 400.

The properties of SAS polishing agents are:

Oil Absorption, Rub-Out Method (cc/100 g)=75-125

BET Surface Area (m² /g)=50-300

MSA Average Aggregate Size (microns)=1-10

Bulk Density (pounds/cu.ft.)=12-35

Compositions 13 through 17 were aged at 49° C. for nine weeks and thetube compatibility properties were evaluated at intervals of 1, 3, 6,and 9 weeks and the results are shown in the following Table 5.

                  TABLE 5                                                         ______________________________________                                        Tube Compatibility Properties, 49° C.                                         Weeks                                                                  Composition                                                                            1         3         6       9                                        ______________________________________                                        13       1         1         1       1                                        14       10        10        10      10                                       15       10        10        10      10                                       16       10        10        10      10                                       17       10        10        10      10                                       ______________________________________                                    

Note that compositions 14 through 17 have excellent tube compatibilityproperties.

What is claimed is:
 1. A method for the production of an abrasivecomposition useful for incorporation into a theraupeutic toothpastecomposition and for preventing fluoride-caused corrosion and staining ofan unlined aluminum tube containing said toothpaste composition, saidabrasive composition comprising a silica which has been treated with awater-soluble alkaline earth metal compound so as to have presenttherein from about 168-7000 ppm of the alkaline earth metal, said silicabeing an amorphous precipitated silica and functioning as a carrier forthe alkaline earth metal;said method comprising the following sequenceof steps:(a) forming an aqueous solution of an alkali metal silicatehaving an SiO₂ to X₂ O mole ratio of about 2.0 to 2.7 and of an alkalimetal sulfate at a reaction temperature in the range of about 66° to 83°C., wherein X represents the alkali metal; (b) acidulating said aqueoussolution with a mineral acid with continuous agitation untilprecipitation of silicon dioxide is substantially complete at a pH ofabout 8.0 to 10.4; (c) continuing the mineral acid addition until the pHis 6.0 or less; (d) digesting at a temperature that is 10°-30° C. higherthan the reaction temperature for a period of about 10 to 30 minutes;(e) filtering the resulting slurry and washing the solid product withfresh water; (f) reslurrying the resulting wet cake in water, and underagitation conditions, adding thereto at ambient temperature a watersoluble alkaline earth metal compound in an amount sufficient to add tosaid wet cake from about 168-7000 ppm of the alkaline earth metal basedon the dry recoverable product; (g) agitating the resulting mixture toprovide adherence of the effective level of said metal on the surface ofsaid silicon dioxide; and (h) drying and recovering said abrasivecomposition.
 2. The method of claim 1 wherein the mineral acid isselected from the group consisting of sulfuric acid, phosphoric acid,nitric acid, hydrochloric acid and carbonic acid.
 3. The method of claim1 wherein the alkaline earth metal is selected from the group consistingof calcium, strontium, magnesium and mixtures thereof.
 4. The method ofclaim 3 wherein the alkaline earth metal is calcium.
 5. The method ofclaim 4 wherein the water-soluble alkaline earth compound is selectedfrom the group consisting of calcium nitrate, calcium oxide, calciumhydroxide and calcium chloride.
 6. The method of claim 1 wherein themineral acid addition in step (c) is continued until the pH is 4.8 to5.0.
 7. The method of claim 1 wherein said abrasive composition is driedby spray drying.
 8. The method of claim 1 wherein the alkali metalsilicate is sodium silicate, the alkali metal sulfate is sodium sulfate,the acidulating acid is sulfuric acid, and the alkaline earth metal isadded in the form of calcium nitrate to provide about 168-7000 ppm ofcalcium in said abrasive composition.
 9. The method of claim 4 whereinthe water-soluble alkaline earth metal compound is selected from thegroup consisting of calcium nitrate, calcium oxide, calcium hydroxide,calcium chloride, calcium formate and calcium acetate.